1. Field of the Invention
The invention relates to a method for producing commercially valuable ultra thin silicon oxide, organic ceramic, or metal oxide films at room temperature and atmospheric pressure. More particularly, the invention relates to the production of such films by exposing a .alpha., .omega.--functional siloxane oligomers or fatty acid metal soaps to short wavelength UV light and ozone.
2. Prior Art
It is known, for example from Klumpp and Sigmund, Photo induced Transformation of Polysiloxane layers to SiO.sub.2, Applied Surface Science 43 (1989) 301-303, to produce silicon oxide layers by treating a polysiloxane vapor deposited layer on a substrate with combined thermal and photolytic conditions. More particularly, a layer of SiO.sub.2 is known to be produceable from the above stated overlayered substrate by subjecting the polysiloxane overlayer to heat in the range of 20-400.degree. C. for hydrolysis and 350-800.degree. C. for condensation. Therefore as a practical matter, the materials must be acted upon at a temperature from about 350.degree. to about 400.degree. C. which is expensive and, therefore, less commercially attractive than the present invention.
Another prior art method includes ultraviolet induced transformation of polysiloxane films. O Joubert, et al in Ultraviolet induced transformation of polysiloxane films J. Appl. Phys. 69 (9), 1 May 1991 pg. 6647-6651 teach that
There are various groups of silicon based organic materials such as the polysiloxanes Si--O.sub.x (C.sub.n H.sub.m).sub.y ! and tetraethoxysilane Si(OC.sub.2 H.sub.5).sub.4 ! which can be used as base materials from which amorphous SiO.sub.2 (a--SiO.sub.2) can be obtained by removal of the CH groups. Forming solutions of a polysiloxane or tetraethoxysilane in the appropriate solvents enables thin films of the materials to be deposited by standard spin-on technology as used for photosensitive resists deposition. The solvents may be removed from the spun films by subsequent heating in air at temperatures in the range from 150 to 250.degree. C. Removal of the CH groups is usually achieved by heating of the dried film at higher temperatures in air or by heating to somewhat lower temperatures in an O.sub.2 plasma. Both processes ensure the reoxidation of the film after CH group removal. Flowing of the remnant, porous films seals the voids and rebounds any dangling bonds let in the network after CH group removal. This process may be achieved by rapid thermal annealing to avoid extended high-temperature effects. Two problems are thus posed in transforming the silicate materials into a--SiO.sub.2 ; removal of the CH groups and void sealing by flow of the network.
The transformation taught, however, requires high temperature and there is no teaching regarding ozone.
A further prior art teaching is from Furjino, et al. in Low temperature and Atmospheric Pressure CVD using Polysiloxane, OMCTS and Ozone, J. Electrochemistry Society, Vol. 138 No. 12 (Dec. 1991) pgs. 3727-3732. Fujino et al teaches that silicon dioxide may be deposited on a substrate by using an organic silicon material, such as OMCTS and ozone at low temperature e.g., 400.degree. C. and atmospheric pressure. Drawbacks of this method include cost associated with low temperature apparatus and an extended period of time required to produce the films. Other drawbacks include substrate depositing onto kept at 400.degree. C. Must heat OMCTS to 80.degree. C. prior to deposition.
Other techniques for preparing silicon oxide films (SiO.sub.x) on various substrates include pyrolytic degradation or UV excimer laser irradiation of polydimethylsiloxanes, chemical and photochemical vapor deposition (commercially available process), and spin casting of silica solutions. All of these techniques involve the use of high temperatures i.e. 100-800.degree. C., to achieve a continuous silicon oxide coating. Also the thickness of these films cannot be made as thin as those prepared from polysiloxane Langmuir-Blodgett films.